Sheet feeder and image forming apparatus using the same

Abstract

A sheet feeder includes a loading member, an attraction separation unit, and a control device. The loading member carries sheet materials. The attraction separation unit includes an endless dielectric belt, holding rollers, and an adjustment device. The endless belt attracts and holds the uppermost one of the sheet materials. The holding rollers holding the endless belt include upstream and downstream holding rollers. The upstream holding roller is rotated around a shaft of the downstream holding roller as the rotation axis in accordance with rotation of the downstream holding roller. The adjustment device provided to the upstream holding roller adjusts the movement range of the upstream holding roller in the height direction. The control device controls, in accordance with the type of sheet materials, an operation of lifting and lowering the loading member, to thereby allow the adjustment device to adjust the movement range of the upstream holding roller.

What is claimed is: 
     
       1. A sheet feeder, comprising:
 a loading member configured to carry a sheet bundle of a plurality of sheet materials loaded thereon; 
 an attraction separation unit including:
 an endless belt made of a dielectric material, and configured to electrostatically attract and hold an uppermost sheet material of the sheet bundle loaded on the loading member, 
 a plurality of holding rollers configured to hold the endless belt, and including an upstream holding roller located on the upstream side in the feeding direction of the sheet materials and a downstream holding roller located on the downstream side in the feeding direction of the sheet materials, the upstream holding roller configured to be pivoted around an axis concentric with a shaft of the downstream holding roller in accordance with rotation of the downstream holding roller, and 
 an adjustment device provided to the upstream holding roller, and configured to adjust the range of vertical movement of the upstream holding roller in the height direction, 
 a stopper member configured to regulate an angle of the endless belt with respect to an upper surface of the sheet bundle; and 
 
 a control device operatively connected to the loading member and configured to control, in accordance with the type of sheet materials to be fed, an operation of lifting and lowering the loading member, to thereby allow the adjustment device to adjust the range of movement of the upstream holding roller in the height direction, 
 wherein the control device controls, in accordance with the type of sheet materials to be fed, the operation of lifting and lowering the loading member, to thereby maintain, a constant separation distance between the upstream holding roller and the upper surface of the sheet bundle loaded on the loading member. 
 
     
     
       2. The sheet feeder according to  claim 1 , wherein the control device controls, in accordance with the type of sheet materials to be fed, a start time of an operation of lifting the loading member to allow the attraction separation unit to start attracting the uppermost sheet material and a start time of an operation of lowering the loading member. 
     
     
       3. The sheet feeder according to  claim 1 , wherein the stopper member is configured to regulate, during separation of the endless belt from the sheet bundle loaded on the loading member, and
 wherein the operation of lifting and lowering the loading member, to maintain the constant separation distance between the upstream holding roller and the upper surface of the sheet bundle loaded on the loading member is during the separation. 
 
     
     
       4. The sheet feeder according to  claim 1 , wherein the control device reduces, in accordance with an increase in rigidity of the sheet materials, the angle of the endless belt with respect to the upper surface of the sheet bundle loaded on the loading member. 
     
     
       5. The sheet feeder according to  claim 1 , further comprising:
 a first detection device configured to detect, on the basis of lifting and lowering of the loading member, the contact of a surface of the endless belt with the upper surface of the sheet bundle loaded on the loading member; and 
 a second detection device configured to detect the position of the upstream holding roller. 
 
     
     
       6. The sheet feeder according to  claim 1 , further comprising:
 a detection device configured to detect, on the basis of lifting and lowering of the loading member, the contact of a surface of the endless belt with the upper surface of the sheet bundle loaded on the loading member, and detect the position of the upstream holding roller. 
 
     
     
       7. The sheet feeder according to  claim 1 , further comprising:
 an operation unit configured to be operated by a user to select the type of sheet materials, 
 wherein the control device controls, in accordance with the type of sheet materials selected through the operation unit, the operation of lifting and lowering the loading member. 
 
     
     
       8. The sheet feeder according to  claim 1 , further comprising:
 a lifting and lowering device configured to perform an operation of lifting and lowering the attraction separation unit, 
 wherein the control device controls the operation of lifting and lowering the attraction separation unit, instead of the operation of lifting and lowering the loading member. 
 
     
     
       9. The sheet feeder according to  claim 8 , wherein the lifting and lowering device performs an operation of lowering the attraction separation unit by causing the attraction separation unit to free fall, and
 wherein the adjustment device includes a movement range regulator configured to regulate the distance of the attraction separation unit falls during freefall of the attraction separation unit. 
 
     
     
       10. An image forming apparatus comprising:
 an image forming unit configured to form an image on a sheet material; and 
 a sheet feeder according to  claim 1  configured to separate an uppermost sheet material from a sheet bundle of a plurality of stacked sheet materials and feed the uppermost sheet material to the image forming unit.